Rubber oxygenases

Abstract

Natural rubber (NR), poly(cis-1,4-isoprene), is used in an industrial scale for more than 100 years. Most of the NR-derived materials are released to the environment as waste or by abrasion of small particles from our tires. Furthermore, compounds with isoprene units in their molecular structures are part of many biomolecules such as terpenoids and carotenoids. Therefore, it is not surprising that NR-degrading bacteria are widespread in nature. NR has one carbon-carbon double bond per isoprene unit and this functional group is the primary target of NR-cleaving enzymes, so-called rubber oxygenases. Rubber oxygenases are secreted by rubber-degrading bacteria to initiate the break-down of the polymer and to use the generated cleavage products as a carbon source. Three main types of rubber oxygenases have been described so far. One is rubber oxygenase RoxA that was first isolated from Xanthomonas sp. 35Y but was later also identified in other Gram-negative rubber-degrading species. The second type of rubber oxygenase is the latex clearing protein (Lcp) that has been regularly found in Gram-positive rubber degraders. Recently, a third type of rubber oxygenase (RoxB) with distant relationship to RoxAs was identified in Gram-negative bacteria. All rubber oxygenases described so far are haem-containing enzymes and oxidatively cleave polyisoprene to low molecular weight oligoisoprenoids with terminal CHO and CO–CH₃ functions between a variable number of intact isoprene units, depending on the type of rubber oxygenase. This contribution summarises the properties of RoxAs, RoxBs and Lcps.

http://bit.ly/2QVVK84

Development and application of a colloidal gold test strip for detection of avian leukosis virus

Abstract

Avian leukosis virus (ALV) is an avian oncogenic retrovirus that induces leukemia-like proliferative diseases in chickens. ALV infection can result in the development of immunological tolerance and persistent viremia. Since effective vaccines against ALV are not yet available, its current prevention primarily depends on detection and eradication to establish exogenous ALV-free poultry flocks. In this study, a rapid and simple colloidal gold test strip method, specific for the group-specific antigen, p27 protein, was developed and systematically evaluated for the detection of ALV from different samples. The detection limit of this assay was as low as 6.25 ng/ml for p27 protein and 80 TCID₅₀/ml for different subgroups of ALV. Besides, the test strip showed high specificity in the detection of different subgroups of ALV, including ALV-A, ALV-B, ALV-J, and ALV-K, with no cross-reaction with other avian pathogens. Furthermore, we artificially infected specific pathogen-free (SPF) chickens with ALV-J, collected cloacal swabs, and examined viral shedding using both test strips and ELISA. Results from the test strip were highly consistent with that from ELISA. In addition, 1104 virus isolates from anti-coagulant blood samples, 645 albumen samples, and 4312 meconium samples were tested, and the test strip results agreed with those of ELISA kit up to 97.1%. All the results indicated that the colloidal gold test strip could serve as a simple, rapid, sensitive, and specific diagnostic method for eradication of ALV in poultry farms.

http://bit.ly/2BOAW83

Isopropylmalate isomerase MoLeu1 orchestrates leucine biosynthesis, fungal development, and pathogenicity in Magnaporthe oryzae

Abstracts

The biosynthesis of branched-chain amino acids (BCAAs) is conserved in fungi and plants, but not in animals. The Leu1 gene encodes isopropylmalate isomerase that catalyzes the conversion of α-isopropylmalate into β-isopropylmalate in the second step of leucine biosynthesis in yeast. Here, we identified and characterized the functions of MoLeu1, an ortholog of yeast Leu1 in the rice blast fungus Magnaporthe oryzae. The transcriptional level of MoLEU1 was increased during conidiation and in infectious stages. Cellular localization analysis indicated that MoLeu1 localizes to the cytoplasm at all stages of fungal development. Targeted gene deletion of MoLEU1 led to leucine auxotrophy, and phenotypic analysis of the generated ∆Moleu1 strain revealed that MoLeu1-mediated leucine biosynthesis was required for vegetative growth, asexual development, and pathogenesis of M. oryzae. We further observed that invasive hyphae produced by the ∆Moleu1 strain were mainly limited to the primary infected host cells. The application of exogenous leucine fully restored vegetative growth and partially restored conidiation as well as pathogenicity defects in the ∆Moleu1 strain. In summary, our results suggested that MoLeu1-mediated leucine biosynthesis crucially promotes vegetative growth, conidiogenesis, and pathogenicity of M. oryzae. This study helps unveil the regulatory mechanisms that are essential for infection-related morphogenesis and pathogenicity of the rice blast fungus.

http://bit.ly/2QYt666

Is marine sediment the source of microbes associated with accelerated low water corrosion?

Abstract

Accelerated low water corrosion (ALWC) is a form of microbiologically influenced corrosion (MIC) associated with the degradation of marine structures around the low tide water level. A better understanding of the role of microbes in this degradation and the source of these microbes is required to improve the prediction and mitigation of the costly failures occurring due to ALWC. The microbial communities present in a sediment sample and on an ALWC tubercle on adjacent steel sheet piling from a tidal estuary were studied using culture-based isolation and metabarcoding. A total of 43 pure cultures were isolated from the sediment using a variety of culture conditions. Phylogenetic analysis of their 16S rRNA genes placed them in the Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria (Alphaproteobacteria and Gammaproteobacteria). 16S rRNA gene metabarcoding of the sediment and tubercle revealed similar microbial groups at varying relative abundances. No Deltaproteobacteria were isolated from the sediment but they were present in both samples according to metabarcoding and their high abundance (49.3%) in the tubercle could indicate an important functional role. Although some sediment isolates and operational taxonomic units from the metabarcoding have previously been associated with surface colonisation or biofilm formation in MIC, there was no strong evidence for the notion that the sediment adjacent to ALWC was the source of tubercle microbes. Further isolation strategies and functional investigations of representative bacteria at different stages of corrosion are being carried out for additional laboratory-based corrosion studies.

http://bit.ly/2BOAR4f

Bioinformatics tools to assess metagenomic data for applied microbiology

Abstract

The reduction of the price of DNA sequencing has resulted in the emergence of large data sets to handle and analyze, especially in microbial ecosystems, which are characterized by high taxonomic and functional diversities. To assess the properties of these complex ecosystems, a conceptual background of the application of NGS technology and bioinformatics analysis to metagenomics is required. Accordingly, this article presents an overview of the evolution of knowledge of microbial ecology from traditional culture-dependent methods to culture-independent methods and the last frontier in knowledge, metagenomics. Topics that will be covered include sample preparation for NGS, starting with total DNA extraction and library preparation, followed by a brief discussion of the chemistry of NGS to help provide an understanding of which bioinformatics pipeline approach may be helpful for achieving a researcher's goals. The importance of selecting appropriate sequencing coverage and depth parameters to obtain a suitable measure of microbial diversity is discussed. As all DNA sequencing processes produce base-calling errors that compromise data analysis, including genome assembly and microbial functional analysis, dedicated software is presented and conceptually discussed with regard to potential applications in the general microbial ecology field.

http://bit.ly/2QVQ2mx

Microbial biosurfactants for oil spill remediation: pitfalls and potentials

Abstract

Spillage of fossil-based oils during their conveyance through water conduits are sporadic, but significant environmental disasters. As the viscous hydrocarbons of the crude oils spread on water surface and choke aquatic life to death, their effective degradation is crucial for ecological balance. Though chemical and mechanical means are conventional ways to tackle the issues, they are riddled with limitations. In this scenario, coercing the biosurfactant-producing bacteria and fungi are promising avenues. Biosurfactants, the amphiphilic compounds, are capable of reducing interfacial tension, dispersing the oil particles, and degrading them into non-toxic debris. Among the vast array of biosurfactants, the trio of rhamnolipid, sophorolipid, and surfactin have been characterized well. Among the microbes, only Pseudomonas, Bacillus, and Candida have been evaluated, while there can be other exploitable candidates. In this regard, this review discusses the scopes and hurdles in utilization of the microbial surface-active compounds for oil spill management.

http://bit.ly/2BOAPt9

Microbial community shifts in biogas reactors upon complete or partial ammonia inhibition

Abstract

Anaerobic digestion of nitrogen-rich substrate often causes process inhibition due to the susceptibility of the microbial community facing ammonia accumulation. However, the precise response of the microbial community has remained largely unknown. To explore the reasons, bacterial communities in ammonia-stressed reactors and control reactors were studied by amplicon pyrosequencing of 16S rRNA genes and the active methanogens were followed by terminal restriction fragment length polymorphism (T-RFLP) analyses of mcrA/mrtA gene transcripts. The results showed that the diversity of bacterial communities decreased in two parallel ammonia-inhibited reactors compared with two control reactors, but different levels of inhibitions coinciding with different community shifts were observed. In one reactor, the process was completely inhibited, which was preceded by a decreasing relative abundance of the phylum Firmicutes. Despite the same operating conditions, the process was stabilized in the parallel, partially inhibited reactor, in which the relative abundance of Firmicutes greatly increased. In particular, both ammonia-inhibited reactors lacked taxa assumed to be syntrophic bacteria (Thermoanaerobacteraceae, Syntrophomonadaceae, and Synergistaceae). Besides the predominance of the hydrogenotrophic methanogens Methanoculleus and Methanobacterium, activity of Methanosarcina and even of the strictly aceticlastic genus Methanosaeta were found to contribute at very high ammonia levels (> 9 g NH₄-N L⁻¹) in the stabilized reactor (partial inhibition). In contrast, the lack of aceticlastic activity in the parallel reactor might have led to acetate accumulation and thus process failure (complete inhibition). Collectively, ammonia was found to be a general inhibitor while accumulating acetate and thus acidification might be the key factor of complete process failure.

http://bit.ly/2QWhtg7

Roles of saprotrophic fungi in biodegradation or transformation of organic and inorganic pollutants in co-contaminated sites

Abstract

For decades, human activities, industrialization, and agriculture have contaminated soils and water with several compounds, including potentially toxic metals and organic persistent xenobiotics. The co-occurrence of those toxicants poses challenging environmental problems, as complicated chemical interactions and synergies can arise and lead to severe and toxic effects on organisms. The use of fungi, alone or with bacteria, for bioremediation purposes is a growing biotechnology with high potential in terms of cost-effectiveness, an environmental-friendly perspective and feasibility, and often representing a sustainable nature-based solution. This paper reviews different ecological, metabolic, and physiological aspects involved in fungal bioremediation of co-contaminated soils and water systems, not only addressing best methods and approaches to assess the simultaneous presence of metals and organic toxic compounds and their consequences on provided ecosystem services but also the interactions between fungi and bacteria, in order to suggest further study directions in this field.

http://bit.ly/2BOAM0r

Polyhydroxyalkanoate synthesis based on glycerol and implementation of the process under conditions of pilot production

Abstract

The present study addresses the synthesis and properties of polyhydroxyalkanoates (PHA) of different composition synthesized by Cupriavidus eutrophus B-10646 using glycerol as a carbon substrate. Poly(3-hydroxybutyrate) [P(3HB)] was effectively synthesized in fed-batch culture in a 30-L fermenter on glycerol of various purification degrees, with 99.5, 99.7, and 82.1% content of the main component. Purified glycerol (99.7%) was used for 150-L pilot scale fermentation. The total biomass and P(3HB) concentration reached 110 and 85.8 g/L, respectively, after 45 h of fed-batch fermentation. An average volumetric productivity of P(3HB) was 1.83 g/(L h). The degree of crystallinity and molecular weight of P(3HB) synthesized on glycerol were lower than and temperature characteristics were the same as those of P(3HB) synthesized on sugars.

http://bit.ly/2R1L7kk

Yeast cultures expressing the Ffase from Schwanniomyces occidentalis , a simple system to produce the potential prebiotic sugar 6-kestose

Abstract

The β-fructofuranosidase Ffase from the yeast Schwanniomyces occidentalis produces potential prebiotic fructooligosaccharides with health-promoting properties, making it of biotechnological interest. Ffase is one of the highest and more selective known producers of 6-kestose by transfructosylation of sucrose. In this work, production of 6-kestose was simplified by directly using cultures of S. occidentalis and Saccharomyces cerevisiae expressing both the wild-type enzyme and a mutated Ffase variant including the Ser196Leu substitution (Ffase-Leu196). Best results were obtained using yeast cultures supplemented with sucrose and expressing the Ffase-Leu196, which after only 4 h produced ~ 116 g/L of 6-kestose, twice the amount obtained with the corresponding purified enzyme. 6-Kestose represented ~ 70% of the products synthesized. In addition, a small amount of 1-kestose and the neofructoligosaccharides neokestose and blastose were also produced. The Ser196Leu substitution skewed production of 6-kestose and neofructooligosaccharides resulting in an increase of ~ 2.2- and 1.5-fold, respectively, without affecting production of 1-kestose. Supplementing yeast cultures with glucose clearly showed that blastose originates from direct fructosylation of glucose, a property that has not been described for other similar proteins from yeasts. Modeling neokestose and blastose into the Ffase-active site revealed the molecular basis explaining the peculiar specificity of this enzyme.

http://bit.ly/2BOAK8P

Streptomyces : implications and interactions in plant growth promotion

Abstract

With the impending increase of the world population by 2050, more activities have been directed toward the improvement of crop yield and a safe environment. The need for chemical-free agricultural practices is becoming eminent due to the effects of these chemicals on the environment and human health. Actinomycetes constitute a significant percentage of the soil microbial community. The Streptomyces genus, which is the most abundant and arguably the most important actinomycetes, is a good source of bioactive compounds, antibiotics, and extracellular enzymes. These genera have shown over time great potential in improving the future of agriculture. This review highlights and buttresses the agricultural importance of Streptomyces through its biocontrol and plant growth-promoting activities. These activities are highlighted and discussed in this review. Some biocontrol products from this genus are already being marketed while work is still ongoing on this productive genus. Compared to more focus on its biocontrol ability, less work has been done on it as a biofertilizer until recently. This genus is as efficient as a biofertilizer as it is as a biocontrol.

http://bit.ly/2EYPHJw

Validation of the Wii Balance Board to assess balance modifications induced by increased respiratory loads in healthy subjects

Publication date: February 2019

Source: Gait & Posture, Volume 68

Author(s): O. Van Hove, A. Van Muylem, D. Leduc, B. Jansen, V. Feipel, S. Van Sint Jan, B. Bonnechère

Abstract

Background

There is a link between breathing and balance and posture. When the inspiratory loads are increased by pathologies, there is a decrease of postural control. The increase of the inspiratory load on respiratory muscles is a common feature in various chronic pulmonary pathologies. Consequently, the balance of those patients is likely affected.

Research question

The aim of this study is to validate the use of the Nintendo Wii Balance Board (WBB) to assess balance modifications induced by increased respiratory loads in healthy subjects.

Methods

Thirty-seven healthy young participants (25 ± 4 years old, 17 women) participated in this study. Five different conditions were tested: without anything (control), throughout a mouthpiece, and throughout three inspiratory threshold loads (ITL) at 10% (low), 40% (mid) and 60% (high) of the maximal inspiratory pressure. Each trial lasted for 60 s. Nine parameters were extracted based on center of pressure displacement based on a previously-validated method. ANOVA tests were used to compare the different conditions followed by Bonferroni's corrections.

Results

Highly statistically significant differences (all p <  0.01) and large effect sizes (all ω² > 0.24) were obtained for all parameters between the different loads and the mouthpiece condition. There is a linear relationship between the load and balance perturbation.

Significance

In this study, we demonstrated the validity of the WBB to detect the effect of the inspiratory load on balance in young healthy subjects. Further studies are needed to determine if such a kind of evaluation can be used in clinics with patients suffering from chronic respiratory disease.

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Validation of the Wii Balance Board to assess balance modifications induced by increased respiratory loads in healthy subjects

Publication date: February 2019

Source: Gait & Posture, Volume 68

Author(s): O. Van Hove, A. Van Muylem, D. Leduc, B. Jansen, V. Feipel, S. Van Sint Jan, B. Bonnechère

Abstract

Background

There is a link between breathing and balance and posture. When the inspiratory loads are increased by pathologies, there is a decrease of postural control. The increase of the inspiratory load on respiratory muscles is a common feature in various chronic pulmonary pathologies. Consequently, the balance of those patients is likely affected.

Research question

The aim of this study is to validate the use of the Nintendo Wii Balance Board (WBB) to assess balance modifications induced by increased respiratory loads in healthy subjects.

Methods

Thirty-seven healthy young participants (25 ± 4 years old, 17 women) participated in this study. Five different conditions were tested: without anything (control), throughout a mouthpiece, and throughout three inspiratory threshold loads (ITL) at 10% (low), 40% (mid) and 60% (high) of the maximal inspiratory pressure. Each trial lasted for 60 s. Nine parameters were extracted based on center of pressure displacement based on a previously-validated method. ANOVA tests were used to compare the different conditions followed by Bonferroni’s corrections.

Results

Highly statistically significant differences (all p <  0.01) and large effect sizes (all ω² > 0.24) were obtained for all parameters between the different loads and the mouthpiece condition. There is a linear relationship between the load and balance perturbation.

Significance

In this study, we demonstrated the validity of the WBB to detect the effect of the inspiratory load on balance in young healthy subjects. Further studies are needed to determine if such a kind of evaluation can be used in clinics with patients suffering from chronic respiratory disease.

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Validation of the Wii Balance Board to assess balance modifications induced by increased respiratory loads in healthy subjects

Publication date: February 2019

Source: Gait & Posture, Volume 68

Author(s): O. Van Hove, A. Van Muylem, D. Leduc, B. Jansen, V. Feipel, S. Van Sint Jan, B. Bonnechère

Abstract

Background

There is a link between breathing and balance and posture. When the inspiratory loads are increased by pathologies, there is a decrease of postural control. The increase of the inspiratory load on respiratory muscles is a common feature in various chronic pulmonary pathologies. Consequently, the balance of those patients is likely affected.

Research question

The aim of this study is to validate the use of the Nintendo Wii Balance Board (WBB) to assess balance modifications induced by increased respiratory loads in healthy subjects.

Methods

Thirty-seven healthy young participants (25 ± 4 years old, 17 women) participated in this study. Five different conditions were tested: without anything (control), throughout a mouthpiece, and throughout three inspiratory threshold loads (ITL) at 10% (low), 40% (mid) and 60% (high) of the maximal inspiratory pressure. Each trial lasted for 60 s. Nine parameters were extracted based on center of pressure displacement based on a previously-validated method. ANOVA tests were used to compare the different conditions followed by Bonferroni’s corrections.

Results

Highly statistically significant differences (all p <  0.01) and large effect sizes (all ω² > 0.24) were obtained for all parameters between the different loads and the mouthpiece condition. There is a linear relationship between the load and balance perturbation.

Significance

In this study, we demonstrated the validity of the WBB to detect the effect of the inspiratory load on balance in young healthy subjects. Further studies are needed to determine if such a kind of evaluation can be used in clinics with patients suffering from chronic respiratory disease.

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Mining data and metadata from the gene expression omnibus

Abstract

Publicly available gene expression datasets deposited in the Gene Expression Omnibus (GEO) are growing at an accelerating rate. Such datasets hold great value for knowledge discovery, particularly when integrated. Although numerous software platforms and tools have been developed to enable reanalysis and integration of individual, or groups, of GEO datasets, large-scale reuse of those datasets is impeded by minimal requirements for standardized metadata both at the study and sample levels as well as uniform processing of the data across studies. Here, we review methodologies developed to facilitate the systematic curation and processing of publicly available gene expression datasets from GEO. We identify trends for advanced metadata curation and summarize approaches for reprocessing the data within the entire GEO repository.

http://bit.ly/2SllZ4q

Effects of Phantom Electrode Stimulation on Vocal Production in Cochlear Implant Users

Objectives: Cochlear implant (CI) users suffer from a range of speech impairments, such as stuttering and vocal control of pitch and intensity. Though little research has focused on the role of auditory feedback in the speech of CI users, these speech impairments could be due in part to limited access to low-frequency cues inherent in CI-mediated listening. Phantom electrode stimulation (PES) represents a novel application of current steering that extends access to low frequencies for CI recipients. It is important to note that PES transmits frequencies below 300 Hz, whereas Baseline does not. The objective of this study was to explore the effects of PES on multiple frequency-related characteristics of voice production. Design: Eight postlingually deafened, adult Advanced Bionics CI users underwent a series of vocal production tests including Tone Repetition, Vowel Sound Production, Passage Reading, and Picture Description. Participants completed all of these tests twice: once with PES and once using their program used for everyday listening (Baseline). An additional test, Automatic Modulation, was included to measure acute effects of PES and was completed only once. This test involved switching between PES and Baseline at specific time intervals in real time as participants read a series of short sentences. Finally, a subjective Vocal Effort measurement was also included. Results: In Tone Repetition, the fundamental frequencies (F0) of tones produced using PES and the size of musical intervals produced using PES were significantly more accurate (closer to the target) compared with Baseline in specific gender, target tone range, and target tone type testing conditions. In the Vowel Sound Production task, vowel formant profiles produced using PES were closer to that of the general population compared with those produced using Baseline. The Passage Reading and Picture Description task results suggest that PES reduces measures of pitch variability (F0 standard deviation and range) in natural speech production. No significant results were found in comparisons of PES and Baseline in the Automatic Modulation task nor in the Vocal Effort task. Conclusions: The findings of this study suggest that usage of PES increases accuracy of pitch matching in repeated sung tones and frequency intervals, possibly due to more accurate F0 representation. The results also suggest that PES partially normalizes the vowel formant profiles of select vowel sounds. PES seems to decrease pitch variability of natural speech and appears to have limited acute effects on natural speech production, though this finding may be due in part to paradigm limitations. On average, subjective ratings of vocal effort were unaffected by the usage of PES versus Baseline. ACKNOWLEDGMENTS: C. J. L. receives grant and research support from Advanced Bionics Corporation and MED-EL Corporation; serves as a consultant for Advanced Bionics, MED-EL, and Oticon Medical; and serves as the Chief Medical Officer of Spiral Therapeutics. The other authors have no other conflicts of interest to disclose. Address for correspondence: Charles J. Limb, 2233 Post Street, 3rd Floor, Rm 325, San Francisco, CA 94115, USA. E-mail: Charles.Limb@ucsf.edu Received June 7, 2017; accepted October 19, 2018. Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.

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Masked Sentence Recognition in Children, Young Adults, and Older Adults: Age-Dependent Effects of Semantic Context and Masker Type

Objectives: Masked speech recognition in normal-hearing listeners depends in part on masker type and semantic context of the target. Children and older adults are more susceptible to masking than young adults, particularly when the masker is speech. Semantic context has been shown to facilitate noise-masked sentence recognition in all age groups, but it is not known whether age affects a listener's ability to use context with a speech masker. The purpose of the present study was to evaluate the effect of masker type and semantic context of the target as a function of listener age. Design: Listeners were children (5 to 16 years), young adults (19 to 30 years), and older adults (67 to 81 years), all with normal or near-normal hearing. Maskers were either speech-shaped noise or two-talker speech, and targets were either semantically correct (high context) sentences or semantically anomalous (low context) sentences. Results: As predicted, speech reception thresholds were lower for young adults than either children or older adults. Age effects were larger for the two-talker masker than the speech-shaped noise masker, and the effect of masker type was larger in children than older adults. Performance tended to be better for targets with high than low semantic context, but this benefit depended on age group and masker type. In contrast to adults, children benefitted less from context in the two-talker speech masker than the speech-shaped noise masker. Context effects were small compared with differences across age and masker type. Conclusions: Different effects of masker type and target context are observed at different points across the lifespan. While the two-talker masker is particularly challenging for children and older adults, the speech masker may limit the use of semantic context in children but not adults. ACKNOWLEDGMENTS: This work was funded by The National Institute on Deafness and Other Communication Disorders R01 DC014460 and T32 DC005360. The authors have no conflicts of interest to disclose. Address for correspondence: Emily Buss, Department of Otolaryngology/Head and Neck Surgery, University of North Carolina, 170 Manning Drive, CB 7070, Chapel Hill, NC 27599, USA. E-mail: ebuss@med.unc.edu Received October 19, 2017; accepted November 5, 2018. Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.

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Effects of Phantom Electrode Stimulation on Vocal Production in Cochlear Implant Users

Objectives: Cochlear implant (CI) users suffer from a range of speech impairments, such as stuttering and vocal control of pitch and intensity. Though little research has focused on the role of auditory feedback in the speech of CI users, these speech impairments could be due in part to limited access to low-frequency cues inherent in CI-mediated listening. Phantom electrode stimulation (PES) represents a novel application of current steering that extends access to low frequencies for CI recipients. It is important to note that PES transmits frequencies below 300 Hz, whereas Baseline does not. The objective of this study was to explore the effects of PES on multiple frequency-related characteristics of voice production. Design: Eight postlingually deafened, adult Advanced Bionics CI users underwent a series of vocal production tests including Tone Repetition, Vowel Sound Production, Passage Reading, and Picture Description. Participants completed all of these tests twice: once with PES and once using their program used for everyday listening (Baseline). An additional test, Automatic Modulation, was included to measure acute effects of PES and was completed only once. This test involved switching between PES and Baseline at specific time intervals in real time as participants read a series of short sentences. Finally, a subjective Vocal Effort measurement was also included. Results: In Tone Repetition, the fundamental frequencies (F0) of tones produced using PES and the size of musical intervals produced using PES were significantly more accurate (closer to the target) compared with Baseline in specific gender, target tone range, and target tone type testing conditions. In the Vowel Sound Production task, vowel formant profiles produced using PES were closer to that of the general population compared with those produced using Baseline. The Passage Reading and Picture Description task results suggest that PES reduces measures of pitch variability (F0 standard deviation and range) in natural speech production. No significant results were found in comparisons of PES and Baseline in the Automatic Modulation task nor in the Vocal Effort task. Conclusions: The findings of this study suggest that usage of PES increases accuracy of pitch matching in repeated sung tones and frequency intervals, possibly due to more accurate F0 representation. The results also suggest that PES partially normalizes the vowel formant profiles of select vowel sounds. PES seems to decrease pitch variability of natural speech and appears to have limited acute effects on natural speech production, though this finding may be due in part to paradigm limitations. On average, subjective ratings of vocal effort were unaffected by the usage of PES versus Baseline. ACKNOWLEDGMENTS: C. J. L. receives grant and research support from Advanced Bionics Corporation and MED-EL Corporation; serves as a consultant for Advanced Bionics, MED-EL, and Oticon Medical; and serves as the Chief Medical Officer of Spiral Therapeutics. The other authors have no other conflicts of interest to disclose. Address for correspondence: Charles J. Limb, 2233 Post Street, 3rd Floor, Rm 325, San Francisco, CA 94115, USA. E-mail: Charles.Limb@ucsf.edu Received June 7, 2017; accepted October 19, 2018. Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.

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Masked Sentence Recognition in Children, Young Adults, and Older Adults: Age-Dependent Effects of Semantic Context and Masker Type

Objectives: Masked speech recognition in normal-hearing listeners depends in part on masker type and semantic context of the target. Children and older adults are more susceptible to masking than young adults, particularly when the masker is speech. Semantic context has been shown to facilitate noise-masked sentence recognition in all age groups, but it is not known whether age affects a listener’s ability to use context with a speech masker. The purpose of the present study was to evaluate the effect of masker type and semantic context of the target as a function of listener age. Design: Listeners were children (5 to 16 years), young adults (19 to 30 years), and older adults (67 to 81 years), all with normal or near-normal hearing. Maskers were either speech-shaped noise or two-talker speech, and targets were either semantically correct (high context) sentences or semantically anomalous (low context) sentences. Results: As predicted, speech reception thresholds were lower for young adults than either children or older adults. Age effects were larger for the two-talker masker than the speech-shaped noise masker, and the effect of masker type was larger in children than older adults. Performance tended to be better for targets with high than low semantic context, but this benefit depended on age group and masker type. In contrast to adults, children benefitted less from context in the two-talker speech masker than the speech-shaped noise masker. Context effects were small compared with differences across age and masker type. Conclusions: Different effects of masker type and target context are observed at different points across the lifespan. While the two-talker masker is particularly challenging for children and older adults, the speech masker may limit the use of semantic context in children but not adults. ACKNOWLEDGMENTS: This work was funded by The National Institute on Deafness and Other Communication Disorders R01 DC014460 and T32 DC005360. The authors have no conflicts of interest to disclose. Address for correspondence: Emily Buss, Department of Otolaryngology/Head and Neck Surgery, University of North Carolina, 170 Manning Drive, CB 7070, Chapel Hill, NC 27599, USA. E-mail: ebuss@med.unc.edu Received October 19, 2017; accepted November 5, 2018. Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.

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Effects of Phantom Electrode Stimulation on Vocal Production in Cochlear Implant Users

Objectives: Cochlear implant (CI) users suffer from a range of speech impairments, such as stuttering and vocal control of pitch and intensity. Though little research has focused on the role of auditory feedback in the speech of CI users, these speech impairments could be due in part to limited access to low-frequency cues inherent in CI-mediated listening. Phantom electrode stimulation (PES) represents a novel application of current steering that extends access to low frequencies for CI recipients. It is important to note that PES transmits frequencies below 300 Hz, whereas Baseline does not. The objective of this study was to explore the effects of PES on multiple frequency-related characteristics of voice production. Design: Eight postlingually deafened, adult Advanced Bionics CI users underwent a series of vocal production tests including Tone Repetition, Vowel Sound Production, Passage Reading, and Picture Description. Participants completed all of these tests twice: once with PES and once using their program used for everyday listening (Baseline). An additional test, Automatic Modulation, was included to measure acute effects of PES and was completed only once. This test involved switching between PES and Baseline at specific time intervals in real time as participants read a series of short sentences. Finally, a subjective Vocal Effort measurement was also included. Results: In Tone Repetition, the fundamental frequencies (F0) of tones produced using PES and the size of musical intervals produced using PES were significantly more accurate (closer to the target) compared with Baseline in specific gender, target tone range, and target tone type testing conditions. In the Vowel Sound Production task, vowel formant profiles produced using PES were closer to that of the general population compared with those produced using Baseline. The Passage Reading and Picture Description task results suggest that PES reduces measures of pitch variability (F0 standard deviation and range) in natural speech production. No significant results were found in comparisons of PES and Baseline in the Automatic Modulation task nor in the Vocal Effort task. Conclusions: The findings of this study suggest that usage of PES increases accuracy of pitch matching in repeated sung tones and frequency intervals, possibly due to more accurate F0 representation. The results also suggest that PES partially normalizes the vowel formant profiles of select vowel sounds. PES seems to decrease pitch variability of natural speech and appears to have limited acute effects on natural speech production, though this finding may be due in part to paradigm limitations. On average, subjective ratings of vocal effort were unaffected by the usage of PES versus Baseline. ACKNOWLEDGMENTS: C. J. L. receives grant and research support from Advanced Bionics Corporation and MED-EL Corporation; serves as a consultant for Advanced Bionics, MED-EL, and Oticon Medical; and serves as the Chief Medical Officer of Spiral Therapeutics. The other authors have no other conflicts of interest to disclose. Address for correspondence: Charles J. Limb, 2233 Post Street, 3rd Floor, Rm 325, San Francisco, CA 94115, USA. E-mail: Charles.Limb@ucsf.edu Received June 7, 2017; accepted October 19, 2018. Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.

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Masked Sentence Recognition in Children, Young Adults, and Older Adults: Age-Dependent Effects of Semantic Context and Masker Type

Objectives: Masked speech recognition in normal-hearing listeners depends in part on masker type and semantic context of the target. Children and older adults are more susceptible to masking than young adults, particularly when the masker is speech. Semantic context has been shown to facilitate noise-masked sentence recognition in all age groups, but it is not known whether age affects a listener’s ability to use context with a speech masker. The purpose of the present study was to evaluate the effect of masker type and semantic context of the target as a function of listener age. Design: Listeners were children (5 to 16 years), young adults (19 to 30 years), and older adults (67 to 81 years), all with normal or near-normal hearing. Maskers were either speech-shaped noise or two-talker speech, and targets were either semantically correct (high context) sentences or semantically anomalous (low context) sentences. Results: As predicted, speech reception thresholds were lower for young adults than either children or older adults. Age effects were larger for the two-talker masker than the speech-shaped noise masker, and the effect of masker type was larger in children than older adults. Performance tended to be better for targets with high than low semantic context, but this benefit depended on age group and masker type. In contrast to adults, children benefitted less from context in the two-talker speech masker than the speech-shaped noise masker. Context effects were small compared with differences across age and masker type. Conclusions: Different effects of masker type and target context are observed at different points across the lifespan. While the two-talker masker is particularly challenging for children and older adults, the speech masker may limit the use of semantic context in children but not adults. ACKNOWLEDGMENTS: This work was funded by The National Institute on Deafness and Other Communication Disorders R01 DC014460 and T32 DC005360. The authors have no conflicts of interest to disclose. Address for correspondence: Emily Buss, Department of Otolaryngology/Head and Neck Surgery, University of North Carolina, 170 Manning Drive, CB 7070, Chapel Hill, NC 27599, USA. E-mail: ebuss@med.unc.edu Received October 19, 2017; accepted November 5, 2018. Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.

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3-D printing of chitosan-calcium phosphate inks: rheology, interactions and characterization

Abstract

Bone substitute fabrication is of interest to meet the worldwide incidence of bone disorders. Physical chitosan hydrogels with intertwined apatite particles were chosen to meet the bio-physical and mechanical properties required by a potential bone substitute. A set up for 3-D printing by robocasting was found adequate to fabricate scaffolds. Inks consisted of suspensions of calcium phosphate particles in chitosan acidic aqueous solution. The inks are shear-thinning and consist of a suspension of dispersed platelet aggregates of dicalcium phosphate dihydrate in a continuous chitosan phase. The rheological properties of the inks were studied, including their shear-thinning characteristics and yield stress. Scaffolds were printed in basic water/ethanol baths to induce transformation of chitosan-calcium phosphates suspension into physical hydrogel of chitosan mineralized with apatite. Scaffolds consisted of a chitosan polymeric matrix intertwined with poorly crystalline apatite particles. Results indicate that ink rheological properties could be tuned by controlling ink composition: in particular, more printable inks are obtained with higher chitosan concentration (0.19 mol·L⁻¹).

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Biofabrication of vessel-like structures with alginate di-aldehyde—gelatin (ADA-GEL) bioink

Abstract

One of the key challenges in the field of blood vessel engineering is the in vitro production of small and large diameter vessels. Considering that a combination of alginate di-aldehyde and gelatin (ADA-GEL) has been successfully applied for different biofabrication approaches, the aim of this study was to exploit ADA-GEL for the fabrication of vessel structures with diameters up to 4 mm. To explore plotting possibilities and to study the swelling behaviour, a library of vessel-like constructs with different diameters made from 2, 3 and 4% (w/v) alginate was created by using various hand-crafted double-needle extrusion systems. Vessel diameters were varied through changes of the double-needle core and outer diameters. A straightforward model for the production of vessel of different diameters from a variety of double-needle systems was established and vessel-constructs with diameters of up to 3.7 mm could be created. It was successfully demonstrated that an artificial vessel, consisting of an outer layer of 7.5% ADA50-GEL50 and an inner core of 3% gelatin, can support the proliferation and migration of an immobilized co-culture containing fibroblast (NHDF) and endothelial (HUVEC) cells. The openness and tightness of the hollow ADA-GEL structures were further confirmed by a dye injection test. Nanoindentation was performed to determine the Young's modulus of the used materials. Cell vitality was proved after 1, 2 and 3 weeks of incubation. The results showed a nearly twofold increase of viable cells per week. Fluorescent images confirmed cell migration during the whole incubation time.

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Sustained release of TGF-β1 via genetically-modified cells induces the chondrogenic differentiation of mesenchymal stem cells encapsulated in alginate sulfate hydrogels

Abstract

Strategies based on growth factor (GF) delivery have attracted considerable attention in tissue engineering applications. Among different GFs, transforming growth factor beta 1 (TGF-β1) is considered to be a potent factor for inducing chondrogenesis. In the present study, an expression cassette encoding the TGF-β1 protein was prepared and transfected into the SP2/0-Ag14 cell line. The confocal microscopy of the transfected cells was performed to confirm the correct transfection process. The expression and in vitro release kinetics of the recombinant TGF-β1 were assessed by western blot analysis and ELISA, respectively. Moreover, the biological activity of the expressed protein was compared with that of a commercially available product. The chondrogenic effects of the sustained release of the recombinant TGF-β1 in an in vitro co-culture system were evaluated using a migration assay and real-time PCR. Results of confocal microscopy confirmed the successful transfection of the vector-encoding TGF-β1 protein into the SP2/0-Ag14 cells. The bioactivity of the produced protein was in the range of the commercial product. The sustained release of the TGF-β1 protein via SP2/0-Ag14 cells encapsulated in hydrogels encouraged the migration of adipose-derived MSCs. In addition, the expression analysis of chondrogenesis-related genes revealed that the pretreatment of encapsulated Ad-MSCs cells in alginate sulfate hydrogels through their exposure to the sustained release of TGF-β1 is an efficient approach before transplantation of cells into the body.

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Keratin nanoparticles-coating electrospun PVA nanofibers for potential neural tissue applications

Abstract

Keratin has the potential to improve biocompatibility and bioactivity of polymeric nanofibers. However, the addition of keratin into the blend nanofiber would decrease the mechanical properties of nanofibers due to the poor spinnability of keratin, and caused inhomogeneous distribution of keratin inside the nanofibers. Therefore, polymeric nanofibers surface-modified with keratin nanoparticles would improve the hydrophility and mechanical property. In this study, keratose (oxidative keratin, KOS) nanoparticles-coating PVA nanofibers (KNPs/PVA) were fabricated by electrospray deposition after electrospinning and acted on neural cells. The chemical conformation, mechanical properties and wettability of KNPs/PVA nanofibers were characterized. The KNPs/PVA nanofibers provided better wettability and stronger mechanical properties compared to KOS/PVA blend nanofibers at the same mass ratio of KOS to PVA. Furthermore, KNPs/PVA nanofibers displayed better cyto-biocompatibility in terms of cell morphology, adhesion and proliferation compared with PVA nanofibers and KOS/PVA blend nanofibers. These results suggested that polymeric nanofibers surface-modified with KOS nanoparticles can provide superior wettability, mechanical properties and biocompatibility by comparison with the blend nanofibers.

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Atypical Asphysia

http://www.jfsmonline.com/article.asp?issn=2349-5014;year=2018;volume=4;issue=4;spage=233;epage=237;aulast=Cao

Forensic investigation of atypical asphysia

Zhe Cao¹, Zhiyuan An², Xiaoning Hou¹, Dong Zhao^3
1 Anshan Public Security Bureau, Anshan, China
² Key Laboratory of Evidence Science (China University of Political Science and Law), Ministry of Education, China, Collaborative Innovation Center of Judicial Civilization, China
³ Key Laboratory of Evidence Science (China University of Political Science and Law), Ministry of Education, China, Collaborative Innovation Center of Judicial Civilization; Key Laboratory of Forensic Genetics of Ministry of Public Security, Institute of Forensic Science, Ministry of Public Security, Beijing, China

Correspondence Address:
Dr. Dong Zhao
25 Xitucheng Road, Haidian, Beijing 100088 
China

Abstract

Smothering, choking, confined spaces, traumatic asphyxia, positional asphyxia, and other kinds of atypical mechanical asphyxia are not rare in forensic practice. However, these are not commonly well demonstrated in forensic monographs worldwide. The authors researched related works and literatures and summarized these with a view to contribute to the existing teaching resources and provide help to forensic practitioners who are involved in scene investigation and identification of such deaths.

Keywords: Asphyxia, forensic pathology, forensic medicine

Introduction

Death caused by compression of the neck, such as from hanging, strangling, or throttling, is termed "mechanical asphyxia" and usually has obvious physical findings. However, asphyxias that result from no direct pressure on the neck vessels or trachea, lack typical morphological changes, or result in minimal damage are called "subtle asphyxias"^[1] or "atypical mechanical asphyxias," used in this article. Atypical mechanical asphyxias include smothering, choking, environmental hypoxia, traumatic asphyxia, and positional asphyxia, among others.

Smothering

Smothering is a form of asphyxia death caused by obstructing the mouth and nose with hands, airtight papers, soft textiles, or the weight of one's own head.^[2]

Smothering can be seen in homicidal or suicidal cases. Homicidal smothering is common in infants, older adults, and people who are unconscious or have restricted motion due to fabric bundling, disease, poisoning, or intoxication. Homicidal smothering can also result when there are significant physical power differences between a perpetrator and victim.^[3],[4],[5] Suicidal smothering is common in psychiatric patients; an example includes wrapping tape around one's mouth, nose, or the entire face.^[6] Smothering can also occur accidentally. For example, adults who are unconscious or paralyzed because of drunkenness, epilepsy, drug overdose, or having another disease might accidentally asphyxiate themselves. Similarly, for an infant lying face down on an airtight mattress or pillow, the weight of the infant's head might obstruct, distort, and occlude his or her mouth and nose, leading to suffocation. In a third example, sleeping infants with clothes or bedding covering their faces are at an increased risk of suffocation.^[1],[2]

In general, it is difficult to identify a case of smothering during forensic scene examination because physical findings are nonspecific.^[7],[8] If smothering is suspected, there may be local signs of pressure on the face.^[2],[3] In adults, with even slight resistance, signs include skin exfoliation from fingernails; contusions on the nose, cheeks, or chin from fingers; bleeding and skin tears corresponding to the teeth in the oral mucosa; and intramuscular bleeding at the mandibular margin. Nasal deformation is also considered a sign of smothering, but can be caused by emergency tracheal intubation.^[3],[5],[7] In infants and adults who are unable to physically resist during asphyxiation, physical damage is difficult to detect.^[3] Of note, a body in the prone position concentrates pressure on the face, preventing accumulation of blood into the compressed skin around the mouth and nose, leading to the formation of distinct pale areas caused by the absence of pooled blood. It is, therefore, important not to assume that pale areas such as these have resulted from indentation by smothering.^[2]

Without positive physical findings in smothering cases, scene investigation plays a decisive role. Pillows and bedding should be examined for blood or lipstick.^[5],[9] For suspected cases of smothering, even if postmortem changes are obvious, suspicious skin lesions should be biopsied for histological examination.^[5] In cases of smothering by textiles, the mouth, nasal cavity, and airways should be examined for inhaled fabric fibers. Fibers in the trachea indicate that a patient may have been alive during smothering.^[8]

Gagging generally involves placing fabric in a victim's mouth to prevent yelling; the fabric gradually becomes soaked with saliva, and if airtight, will lead to suffocation. Another form of gagging involves placing tape over the mouth or nose, which results in trapped mucus production that eventually leads to suffocation. Obstruction of the nasopharynx by objects in the oral cavity may also lead to gagging and subsequent death.^[2] Usually, suspected gagging is confirmed when blocking objects are found, not by any specific physical signs of asphyxia.^[3]

Choking

Choking refers to upper respiratory tract blockage by a foreign body leading to suffocation. The foreign body is usually lodged between the larynx and trachea.^[10],[11] Death may result from simple hypoxia; however, many deaths occur quickly before the onset of hypoxia. Studies have found that, even in cases in which the airway is not completely blocked, death often occurs, likely from neurogenic-induced cardiac arrest.^{[2],[9],[11],[12]}

Choking is almost always accidental, with cases of homicide and suicide relatively rare.^[1],[11] For infants, accidental choking most often occurs with foreign body ingestion; for adults, choking most often occurs with food.^[1],[11] Victims in homicidal choking cases are most likely to be older adults, infants, young children, people who are unconscious, or persons debilitated by illness or intoxication. Suicidal choking most often occurs in patients with psychosis or prisoners in jail.^[1]

Evidence of coughing helps eliminate choking as a cause of death because it signifies that the respiratory tract was open during upper respiratory blockage.^[3] Computed tomography imaging can provide information before an autopsy on the location of a foreign body and can help inform an autopsy plan.^[13] Few physical findings are generally seen in choking deaths, so the discovery of a foreign body in the airway, a detailed clinical history, descriptions of the death environment and any resuscitation attempts, and exclusion of other causes of death are critical when forming a conclusion.^{[1],[9],[11],[12]} If the foreign body shifts during resuscitation or otherwise is moved, clinical history might be the only evidence.^[3],[13]

Foreign bodies blocking the airway leading to choking generally belong to the following categories.^[2]

Foreign objects

Attackers may put a towel or sock into the victim's mouth to prevent shouting; this can cause choking and gagging.^[3] In another example, people may inhale sand, piles of gravel, or piles of soil when they fall on them, causing respiratory blockage and resulting in choking death. This scenario may occur accidentally at a construction site, during a traffic accident, or in children playing in or eating sand.^[3],[14]

Acute obstruction

Acute allergy, steam stimulation, heat inhalation, and acute inflammation may cause swelling of the throat organs, including the epiglottis, tonsils, or glottis, leading to choking. Trauma in the anterior or lateral cervical neck structures can also result in severe swelling of the respiratory tract from bleeding and edema.^[1],[2],[7] Tumors, polyps, or cysts can also block respiration, leading to choking.^{[1],[10],[11]}

Foods

The most common foreign bodies causing choking death in adults are foods.^[10] Susceptible factors include old age, neuromuscular disease, poor dentition leading to chewing problems, consumption of alcohol or other central nervous system depressants weakening the gag reflex, or other neurological or mental illness (of which poor dentition is an important risk factor).^{[1],[11],[12],[13]} Of patients with mental illness, those with schizophrenia are most likely to choke on food, possibly from a propensity to swallow incompletely chewed food.^[11] The majority of adult choking cases occur at patients' homes, nursing homes, or mental hospitals, and often take place suddenly during meals.^[1]

When a sudden death occurs while eating or soon after, the possibility of choking must be considered. A search for a blocked airway should be initiated, but in addition, the investigator should also consider factors that could have aggravated the choking episode. Therefore, quality and number of teeth, food debris in the esophagus – which can cause tracheal obstruction from the external oppression – and exclusion of neurological diseases and intoxication are all important when evaluating sudden death during a meal.^{[1],[9],[11],[12]}

It is typical for gastric contents to be present in the throat, trachea, and bronchi after death, caused by reflux or shifting of contents. This is a common postmortem phenomenon, found in 20%–25% of routine examinations. As a result, if a small amount of gastric content is found in the respiratory tract, this does not mean that choking had occurred; however, if the throat or airway is completely blocked by gastric contents, choking can be concluded.^[2],[3],[13] The inhalation of gastric contents is more common in people who are unconscious.^[1]Importantly, there is no reliable way to distinguish natural food reflux early in the dying process from true inhalation while alive, unless the inhalation occurred during a clinical procedure or another person witnessed the event. In most cases, in the absence of hard evidence, it is unreasonable for forensic officers to conclude that the inhalation of gastric contents is secondary to choking death.^[2]

Environmental Hypoxia

Environmental asphyxiation is usually caused by a lack of oxygen in the local environment,^[1],[2],[3] and is almost always accidental. Oxygen deficiency can occur secondary to breathing exercises, microbial consumption, activities related to industrial work (such as welding), environmental chemical reactions (such as rust), absorption by chemical substances (such as activated carbon), and presence of toxic gases (such as propane, nitrogen, and methane).^[1],[2],[3] An atmospheric oxygen concentration below 5%–10% will cause death in a few minutes, and a concentration of carbon dioxide higher than 10% is lethal.^[1] In some cases, death occurs before the onset of hypoxia, and is secondary to overexcitement of the body's chemical sensing system, which causes parasympathetic nervous system-mediated cardiac arrest.^[2]

In hypoxia-asphyxia deaths caused by low atmospheric oxygen levels, physical findings are usually absent,^[2] making elucidation of the specific cause of death difficult. Investigators must carefully analyze the environment and exclude other causes of death to conclude environmental hypoxia-asphyxia.^[3] Measurements of toxic gases and oxygen concentrations in the air, as well as postmortem analysis of blood and tissues, should be performed; in addition, scene simulations may be required.^[1]

As a type of environmental hypoxia-asphyxia, plastic bag suffocation is often used as a suicide technique in Western countries. This method is common in young men and elderly women.^[15] Some people even use the propane, ether, or helium gas along with the plastic bag. Plastic bag suffocation deaths can also occur accidentally or unexpectedly, such as during sexual asphyxia, children playing with plastic bags, and other occurrences.^[1] It is very rare for the use of plastic bags to result in death; however, it is more likely in cases in which the victim is unconscious, or when there is a large difference in strength between the perpetrator and victim.^[16]

Plastic bag suffocation often occurs rapidly with few physical signs;^[1],[2] however, in a small number of cases, marks on the neck are present corresponding to the areas of bag bundling (such as from a rubber band), or there may be signs of prior injury, such as wrist cutting or abuse.^[1],[2] It is a common misconception that the postmortem presence of moisture in the plastic bag confirms that the bag was placed on a breathing human; water droplets form as gas evaporates from the skin, nose, and mouth even if the person was previously deceased.^[2]

Because there are usually no specific physical findings, it is difficult to identify cases of plastic bag suffocation unless the bag is over the head at the time of scene investigation or autopsy.^[2] If the plastic bag is removed before forensic workers see the corpse, they will not be able to determine the cause of death through forensic examination, and may even conclude that a natural death occurred. Therefore, to identify such cases, forensic workers must pay careful attention during scene exploration and investigation.^{[1],[3],[9],[16]} If necessary, forensic workers can conduct simulations under close monitoring in a protected environment, which can help to pinpoint a cause of death through analysis of time measurements.^[4],[6],[17] Specimens collected from the blood, lungs, liver, or other organs for poison analysis should be extracted and stored in a sealed empty bottle along with a plastic bag,^[2],[7],[16] frozen, and delivered promptly.^[1]

Traumatic Asphyxia

Traumatic asphyxia refers to the compression of the chest or abdomen by massive mechanical forces resulting in thoracic fixation – expansion of thoracic and lower phrenic muscles – leading to respiratory disturbance and death by asphyxiation.^[2]

Traumatic asphyxia is common in the following types of accidents: motor vehicle compression or extrusion during traffic accidents; pinning from building collapse, falling rocks, or other objects; trampling by a crowd; compression while standing in a crowded population from sudden external forces; compression by fallen tools or furniture; and compression of infants and children while sleeping with parents (overlaying asphyxia).^[1],[2],[18] There are also reports of homicide resulting from a perpetrator kneeling or sitting on the chest of a victim.^[19]

The pathological features of traumatic asphyxia are usually quite specific. These include prominent facial and nuchal hyperemia and swelling; numerous petechial hemorrhages on the face or conjunctiva; subconjunctival hemorrhage and edema; and nasal bleeding. In general, a person who dies from traumatic asphyxiation often appears strangled with features extending down to the neck, with no signs of local damage.^{[2],[20],[21]}

However, physical features such as these are not always visible. Studies have shown that, in up to 10% of cases, no petechial hemorrhages are seen on the face or conjunctiva. The reason for this is unclear, but may be related to rapidness of death, lack of obvious chest compression or vagus nerve stimulation, lack of occlusion of the epiglottis, or concurrence of both left heart and right heart impairment at the time of chest compression.^{[1],[18],[20],[21]} On gross examination, lungs may have a purplish red color, congestion, or subserous bleeding with or without obvious expansion of the right heart or superior vena cava; sometimes, there is no evidence of trauma despite severe direct external compression on the chest and abdomen.^{[1],[2],[3],[9]}

Traumatic asphyxia is a diagnosis of exclusion. In addition to supporting evidence from a scene investigation, suffocation death should only be considered after excluding fatal injuries and poisoning.^[1],[9],[21]

Overlaying asphyxia is a special form of traumatic asphyxia, often secondary to nasal compression. Physical examination findings are usually absent, so overlaying can be difficult to determine unless the same-bed sleeper admits to crushing the infant or child. Overlaying asphyxia is sometimes attributed to sudden infant death syndrome, so it is important to examine adults' and children's clothes and bedding carefully as well as the scene.^[1],[3],[22]

Positional Asphyxia

Positional asphyxia refers occurrences in which respiration is compromised from splinting of the chest or diaphragm preventing normal respiration, or occlusion of the upper airway due to abnormal positioning of the body.^[23] Positional asphyxia is almost always an accident, during which the victim cannot extract himself or herself from a specific position or small space. The victim may be further impaired by alcohol or drug intoxication, weakness, neurological disease, or fabric bundling. Common examples of positional asphyxia include limbs tied behind the back while in a prone position (may be performed for restraint by police or psychiatrists for suspects or patients); head-down position (inversion of the body, or head hanging down off the edge of a bathtub); jack-knife position (upper body significantly curved from the waist down); bundled thoracic or abdominal horizontal sling (e.g., a young girl wearing a belt hanging by the abdomen on a swing); excessive flexion or extension of the neck (e.g., during a motor vehicle accident); lack of chest wall expansion in a restricted space (wedging); and a person sandwiched between the wall and the mattress after falling off the bed.^{[1],[2],[3],[4],[5],[6],[7],[24]} A typical case of postural asphyxia involves a drunken person who collapses into a narrow space, excessively distorting the neck and hindering breathing, leading to death.^[9]

Cause of death from positional asphyxia often results from reverse suspension of the body such that the movement of the chest wall is restricted by intra-abdominal organs compressing the diaphragm. This prolongs inspiration, and eventually results in respiratory muscle fatigue, leading to slowed movement of the chest wall and subsequent hypoxia. Venous return is effectively limited, and blood flow to the brain is shifted, decreasing blood flow and further aggravating respiratory muscle fatigue; eventually, the heart stops.^[1] Positional asphyxia does not require reversal of the entire body; fatal asphyxia may result from the reversal of torso position, excessive flexion of the neck, or pressure on one's face, such as in an intoxicated person whose face is pressed to the floor.^[25] The difference between traumatic asphyxia and positional asphyxia is whether the chest and abdomen are compressed by external forces. If chest compression is from an external source, he or she should have been died from traumatic asphyxia. If a deceased person is found in a specific position or restricted space that limits chest activity, the person should have been died from positional asphyxia.^[1],[23]

Positional asphyxia can be identified by the following criteria: The body position is consistent with restricted or disordered respiration; scene investigation or historical investigation identifies that an accident had occurred; the deceased person cannot change his or her position for some reason; and other obvious natural or violent causes of death are excluded. A diagnosis of accidental positional asphyxia mainly depends on the evidence obtained from the scene environment.^[24],[25] Some forensic investigators believe that, if another disease is present, then either the cause of death is not associated with positional asphyxia, or the onset of the disease makes the deceased patient prone to positional asphyxia.^[23] It should be noted that alcohol consumed by a patient with positional asphyxia may be metabolized. Thus, even if the concentration of alcohol in the blood or urine is very low or negative, the possibility of positional asphyxia cannot be ignored.^[24]

Wedging is a special form of positional asphyxia, commonly seen in infants and young children whose body or head are compressed in a narrow space. The chest wall is fixed, resulting in airway obstruction that results in asphyxia. Wedging usually occurs between a mattress and wall or mattress and furniture or baby crib. It is most common in infants aged 3–6 months, intoxicated adults, or comatose patients who accidentally fall between a mattress and wall, leading to death. Physical findings of wedging are usually absent.^[1],[22]

Acknowledgments

This study was supported by the Open Project of Key Laboratory of Forensic Genetics, Ministry of Public Security (2017FGKFKT05), Program for Young Innovative Research Team from China University of Political Science and Law (2016CXTD05), and Project of Interdisciplinary Science Construction-Forensic Psychology from China University of Political Science and Law.